Preparation of lacing resistant, titanium dioxide particles for use in photodurable thin film production

ABSTRACT

A process is provided for the preparation of lacing resistant, titanium dioxide particles for use in photodurable thin film production. Said process involves dewatering titanium dioxide particles that have been encapsulated with a layer of amorphous alumina in continuous fashion at temperatures in excess of 100° C.

This application is a continuation of Ser. No. 16/100,254, filed Aug.10, 2018, now allowed, which is a divisional application of U.S. Ser.No. 14/930,731 filed Nov. 3, 2015, which claims priority of U.S.Provisional Application No. 62/076,158 filed Nov. 6, 2014.

FIELD OF THE INVENTION

Disclosed are methods for the efficient production of lacing resistanttitanium dioxide particles that can be used to produce thin films thatpossess photodurable properties.

BACKGROUND OF THE INVENTION

Titanium dioxide particles of the rutile or anatase crystalline formpossess a well-known characteristic ability to absorb light in theultraviolet (UV) wavelength range, a process that generates metastableelectron poor and electron rich regions within the particle structure.If the surfaces of said particles are not suitably modified, theinteraction of water and/or oxygen with said regions results in thegeneration of highly reactive, oxygen atom-based radical species thatcan over time degrade the appearance and/or the physical properties ofmany of the thermoplastic polymer matrices into which the aforementionedparticles might be incorporated (see D. Holtzen, P. Niedenzu, M.Diebold, “TiO2 Photochemistry and Color Applications”, Society ofPlastics Engineers' 2001 Annual Technical Conference Proceedings). Putdifferently, unless suitably modified, the UV light inducedphotoactivity of titanium dioxide particles for the most part preventstheir use for the manufacture of thermoplastic polymer derived articlesthat require a commercially useful level of photodurability. Commonexamples of thermoplastic polymer matrices that are typically affectedby this problem include, but are not limited to, those based onpolyethylene, polypropylene and polyvinyl chloride.

A surface modification technique that is most often utilized during thecommercial production of titanium dioxide particles to effectivelymitigate the aforementioned photoactivity involves the encapsulation ofsaid particles in a layer of amorphous silica which is then followed bythe deposition of crystalline alumina of boehmite or boehmite-likemorphology. An example of such a particle encapsulation process istaught in U.S. Pat. No. 5,993,533. The amorphous silica portion of thistype of particle treatment is typically present at levels that rangefrom about 1 wt % to about 10 wt % (total particle basis) while thecrystalline alumina portion of said treatment is typically present atlevels that range from about 1 wt % to about 5 wt % (total particlebasis).

Another surface modification technique that can be employed tosignificantly mitigate the undesirable photoactivity of titanium dioxideparticles involves encapsulating them in a layer of only amorphousalumina. An example of such a particle encapsulation process is taughtin Example 1 of U.S. Pat. No. 4,460,655. In this process, fluoride ion,typically present at levels that range from about 0.05 wt % to 2 wt %(total particle basis), is used to disrupt the crystallinity of thealumina, typically present at levels that range from about 1 wt % toabout 8 wt % (total particle basis), as the latter is being depositedonto the titanium dioxide particles. Note that other ions that possessan affinity for alumina such as, for example, citrate, phosphate orsulfate can be substituted in comparable amounts, either individually orin combination, for the fluoride ion in this process.

A significant disadvantage of the amorphous silica/crystalline aluminaand the amorphous alumina-only particle encapsulation strategies is thatthe resulting particle encapsulations are prone to water retentionand/or latent water generation. These tendencies can lead to the releaseof water vapor when the so-encapsulated titanium dioxide particles areincorporated into thermoplastic polymer derived articles using elevatedtemperatures. Such a release can unfortunately result in the formationof commercially unacceptable defects in the article that is beingproduced. When the article that is being produced is in thin film form,undesirable thin spots and/or holes can be produced in the film as it isbeing extruded, a process that is typically referred to as lacing.

SUMMARY OF THE INVENTION

Surprisingly, it has been found that the lacing resistance of amorphousalumina-only encapsulated titanium dioxide particles can be increased toa commercially useful level by simply dewatering said particles incontinuous fashion using readily available particle drying equipment ata temperature greater than 100° C., most preferably, from 200° C. to500° C., a behavior that was not observed when amorphoussilica/crystalline alumina encapsulated titanium dioxide particles weresubjected to a similar dewatering treatment. Importantly, the ability ofthe amorphous alumina-only encapsulated titanium dioxide particles toresist the generation of oxygen based radical species when exposed to UVlight radiation is not compromised by application of the dewateringprocess.

One embodiment of the present invention is a method of making lacingresistant, low photoactivity titanium dioxide particles comprising thesteps of: a) providing titanium dioxide particles encapsulated withamorphous alumina; and b) heating the titanium dioxide particlesencapsulated with amorphous alumina to a temperature above 100° C. toform dewatered particles. The titanium dioxide particles may also beheated to a temperature in the range of 200° C. to 500° C. The titaniumdioxide particles produced from this process may undergo an additionalstep of treating the surface of the dewatered particles with an organiccompound selected from the group consisting of low molecular weightpolyols, organosiloxanes, organosilanes, alkylcarboxylic acids,alkylsulfonates, organophosphates, organophosphonates and mixturesthereof. The preferred organic compound is selected from the groupconsisting of low molecular weight polyols, organosiloxanes,organosilanes and organophosphonates and mixtures thereof and theorganic compound is present at a loading of between 0.20 wt % and 2.00wt % on a total particle basis.

Another embodiment of the present invention is a method of making amasterbatch comprising the steps of: a) providing titanium dioxideparticles encapsulated with amorphous alumina; b) heating the titaniumdioxide particles encapsulated with amorphous alumina to a temperatureabove 100° C. to form dewatered particles or preferably to a temperaturein the range of 200° C. to 500° C.; c) treating the surface of thedewatered particles with an organic compound to form treated particles;and d) mixing the treated particles with a thermoplastic polymer to makea masterbatch.

Another embodiment of the present invention is a method of making anarticle comprising the steps of: a) providing titanium dioxide particlesencapsulated with amorphous alumina; b) heating the titanium dioxideparticles encapsulated with amorphous alumina to a temperature above100° C. to form dewatered particles; c) treating the surface of thedewatered particles with an organic compound to form treated particles;d) mixing the treated particles with a thermoplastic polymer to make amasterbatch; e) mixing the masterbatch with additional thermoplasticpolymer; and f) forming an article. The article may be a film having athickness from 7 microns to 200 microns, preferably from 7 microns to 50microns.

Another embodiment of the present invention is a composition of mattercomprising titanium dioxide particles encapsulated with amorphousalumina wherein said particles possess a water content of 0.65 wt % orless on a total particle basis.

Another embodiment is a composition comprising: a) titanium dioxideparticles encapsulated with amorphous alumina wherein said particlespossess a water content of 0.65 wt % or less on a total particle basis;and

b) a thermoplastic polymer. The composition preferably is a masterbatchor a film.

DETAILED DESCRIPTION OF THE INVENTION

Applicants specifically incorporate the entire content of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, a preferredrange, or a list of upper preferable values and lower preferable values,this is to be understood as specifically disclosing all ranges formedfrom any pair of any upper range limit or preferred value and any lowerrange limit or preferred value, regardless of whether ranges areseparately disclosed. Where a range of numerical values is recitedherein, unless otherwise stated, the range is intended to include theendpoints thereof, and all integers and fractions within the range. Itis not intended that the scope of the invention be limited to thespecific values recited when defining a range.

Titanium dioxide particles that are suitable for this invention arethose that possess the following: most preferably, no organic surfacetreatment; an average particle size of about 20 nanometers to about 1000nanometers, preferably from about 100 nanometers to about 750 nanometersand more preferably from about 200 nanometers to about 500 nanometers;the anatase or rutile crystalline form; and one or more particleencapsulating layers of amorphous alumina without said particles beingpre-encapsulated with silica.

The dewatering process can be efficiently performed by passing thetitanium dioxide particles suitable for this invention in continuousfashion through a pre-heated, gravity discharge, non-contact rotarycalciner such as those produced by Heyl & Patterson's Renneburg Division(Pittsburgh, Pa.). Calciners of this type typically employ acounter-current air flow to remove volatilized water and can be heatedelectrically, with steam or via the use of a heated liquid medium suchas oil. An adjustable rate pigment feeding mechanism at the entrance tothe calciner and an adjustable dam at the outlet of the calciner intandem provide a means to alter the residence time of pigment within thecalciner so as to provide for the desired degree of pigment dewateringfor a given operating temperature. For the latter parameter, preferredtemperatures include those greater than 100° C. and, most preferably,those from 200° C. to 500° C. The dewatered amorphous aluminaencapsulated titanium dioxide particles produced by the method of thisinvention possess a water content (total particle basis) of 0.65 wt % orless, more preferably 0.55 wt % or less and most preferably 0.50 wt % orless.

The dewatering process can also be performed in a batch calciner basedunit operation but such a process is typically less cost-effective thanusing the continuous process described above.

Following the dewatering step, any organic based surface treatment canbe added to the dewatered pigment particles at a loading (total particlebasis) of between 0.05 and 5.00 wt %, more preferably between 0.10 wt %and 3.00 wt % and most preferably between 0.20 and 2.00 wt %, as long assaid treatment does not contribute to the generation of theaforementioned lacing imperfections. The treatment of inorganicparticles such as titanium dioxide with organic compounds is well knownas a means to allow the efficient incorporation of said particles intopolymer matrices at high loadings, at high processing rates and with ahigh degree of dispersion (see, for example, U.S. Pat. Nos. 5,607,994;5,631,310; 5,889,090; and 5,959,004, the contents of which areincorporated herein by reference). Examples of organic compounds thatcan be used in this treatment step, either individually or incombination, include, but are not limited to, low molecular weightpolyols, organosiloxanes, organosilanes, alkylcarboxylic acids,alkylsulfonates, organophosphates or organophosphonates.

By dewatered pigment particles, it is meant that said particles havelost water after undergoing the heating process of the current inventionsuch that their lacing resistance is enhanced.

The dewatered pigment particles of the current invention, which may ormay not possess an organic compound derived surface treatment, can beincorporated into a wide variety of thermoplastic polymers to makemasterbatch which in turn can then be combined with additionalthermoplastic polymer prior to making a final article of desired form.In the case of masterbatch production, the pigment and thermoplasticpolymer can be combined using, for example, continuous mixer, batchmixer and twin screw extrusion production technologies. The combinationof masterbatch and additional thermoplastic polymer can then beconverted into a final desired article using, for example, cast filmextrusion, blown film extrusion, slit film extrusion, sheet and profileextrusion, fiber and filament extrusion, film coating extrusion and wirecoating extrusion technologies as well as injection molding, blowmolding, blown film molding and rotational molding technologies.

By thermoplastic, it is meant that a polymer can be repeatedlymanipulated in a processing step that involves obtaining the polymer inthe molten state. The term masterbatch refers to a pigment andthermoplastic polymer combination that possesses a pigment loading of 50wt % to 85 wt %, more preferably a pigment loading of 60 wt % to 75 wt%.

During the masterbatch and final shaped article production processes,additives known in the art to provide beneficial properties to themasterbatch and to said article such as, for example, antioxidants,light stabilizers, colorants, surface friction modifiers, lubricants,anti-blocking agents, anti-static agents or other pigments, can beincorporated as well, either individually or in combination, usingtechniques known in the art.

Thermoplastic polymers that can be used in the above mentionedproduction processes include, but are not limited to, the following:polymers derived from ethylenically unsaturated monomers includingolefins such as polyethylene, polypropylene, polybutylene, andcopolymers of ethylene with other olefins such as vinyl acetate or alphaolefins containing 4 to 10 carbon atoms; vinyls such as polyvinylchloride; polyvinyl esters such as polyvinyl acetate; polystyrene;acrylonitrile-butadiene-styrene; acrylic homopolymers and copolymers;phenolic polymers and copolymers; alkyd and amino resins; epoxy resins,polyamides, polyurethanes; phenoxy resins, polysulfones; polycarbonates;polyesters and chlorinated polyesters; polyethers; acetal resins;polyimides; and polyoxyethylenes. Mixtures of polymers are alsocontemplated. Thermoplastic polymers suitable for use in the presentinvention also include various rubbers and/or elastomers and eithernatural or synthetic polymers based on copolymerization, grafting, orphysical blending of various diene monomers with the above-mentionedpolymers, all as generally known in the art. Typically, thethermoplastic polymer may be selected from the group consisting ofpolyolefin, polyvinyl chloride, polyamide, polyester and polycarbonateand mixtures thereof. More typically used thermoplastic polymers arepolyolefins. Most typically used thermoplastic polymers are polyolefinsselected from the group consisting of polyethylene, polypropylene andmixtures thereof. Typical polyethylene polymers are low densitypolyethylene and linear low density polyethylene.

While the compositions and methods of this invention have been describedin terms of preferred embodiments, it will be apparent to those of skillin the art that variations may be applied to the compositions andmethods and to the steps or to the sequence of steps of the methoddescribed herein without departing from the concept, spirit, and scopeof the invention. More specifically, it will be apparent that certainagents which are chemically related may be substituted for the agentsdescribed herein while the same or similar results would be achieved.All such similar substitutes and modifications apparent to those skilledin the art are deemed to be within the spirit, scope, and concept of theinvention as defined by the appended claims.

EXAMPLES

The present invention is further defined in the following Examples. Itshould be understood that these Examples, while indicating preferredembodiments of the invention, are given by way of illustration only.From the above discussion and these Examples, one skilled in the art canascertain the preferred features of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various uses andconditions.

All of the inorganic and organic titanium dioxide particle surfacetreatment loadings provided in the below examples are on a totalparticle basis. The carbon content of the octyltriethoxysilane (OTES)treated pigment samples was determined using a LECO SC632 Analyzer. Themoisture content of pigment samples that did not possess an OTES surfacetreatment were obtained using a Perkin Elmer TGA 7 ThermogravimetricAnalyzer operating as follows:

-   -   1. Under flowing air (50 mL/minute), 10-20 mg of pigment sample        is heated from room temperature to 316° C. at a 100° C./minute        heating rate.    -   2. Said sample is then held at 316° C. for 30 minutes.    -   3. The total mass loss of said sample after completion of the        hold period is then determined.

Example 1

Fifty kilograms of organic surface treatment free, pigmentary sized,titanium dioxide particles of the rutile crystalline phase that had beenencapsulated with 1.8 wt % amorphous alumina according to the teachingof U.S. Pat. No. 4,460,655, the contents of which are incorporatedherein by reference, otherwise known as the starting pigment, weredewatered in a Heyl and Patterson built, non-contact rotary calciner(heating zone tube dimensions: 7 feet long×0.54 feet wide, cooling zonetube dimensions: 3 feet long×0.54 feet wide; 2.5% calciner tube slope)using a counter-current air flow, a calciner temperature of 338° C. anda pigment residence time within said calciner of 5 minutes. Saidcalciner was rotated at about 5 rpm during the dewatering process.Thermogravimetric analysis of the dewatered pigment particles yielded amoisture content of 0.47 wt %.

Ten kilograms of the dewatered pigment particles were then placed intoan aluminum foil lined metal pan and treated with neatoctyltriethoxysilane (OTES) at a 1.0 wt % loading using a hand spryer.The OTES-treated pigment particles were then air dried at roomtemperature for 48 hours, homogenized in a V-cone blender and finallydeagglomerated using an 8 inch steam micronizer at 290° C. using asteam-to-pigment ratio of 7-to-1. The resulting product was labeled asSample A1 and possessed an OTES-derived carbon content of 0.298 wt %.

The OTES treatment and subsequent particle deagglomeration process wasthen repeated using a second 10 kilogram batch of dewatered pigmentparticles to give product that was labeled as Sample A2 and thatpossessed an OTES-derived carbon content of 0.312 wt %.

Example 2

Ten kilograms of the starting pigment utilized in Example 1 were treatedwith OTES and then deagglomerated using the same procedures as describedin said Example to yield a final product that was labeled as Sample B1and that possessed an OTES-derived carbon content of 0.288 wt %. Priorto the OTES addition, the starting pigment was found bythermogravimetric analysis to possess a moisture content of 1.12 wt %.

The OTES treatment and subsequent deagglomeration process was thenrepeated using a second 10 kilogram batch of starting pigment to giveproduct that was labeled as Sample B2 and that possessed an OTES-derivedcarbon content of 0.319 wt %.

Comparative Example 3

Fifty five kilograms of organic surface treatment free, pigmentarysized, titanium dioxide particles of the rutile crystalline phase thathad been sequentially encapsulated with 3.2 wt % amorphous silica andthen with 1.9 wt % pseudo-boehmite alumina according to the teaching ofU.S. Pat. No. 5,993,533, the contents of which are incorporated hereinby reference, otherwise known as the starting pigment, were dewatered ina Heyl and Patterson built, non-contact rotary calciner (heating zonetube dimensions: 7 feet long×0.54 feet wide, cooling zone tubedimensions: 3 feet long×0.54 feet wide; 2.5% calciner tube slope) usinga counter-current air flow, a calciner temperature of 330° C. and apigment residence time within said calciner of 5 minutes. Said calcinerwas rotated at about 5 rpm during the dewatering process.Thermogravimetric analysis of the dewatered pigment particles yielded amoisture content of 0.65 wt %.

Ten kilograms of the dewatered pigment particles were then placed intoan aluminum foil lined metal pan and treated with neat OTES at a 1.0 wt% loading using a hand spryer. The OTES-treated pigment particles werethen air dried at room temperature for 48 hours, homogenized in a V-coneblender and finally deagglomerated using an 8 inch steam micronizer at290° C. using a steam-to-pigment ratio of 7-to-1. The resulting productwas labeled as Sample C1 and possessed an OTES-derived carbon content of0.301 wt %.

The OTES treatment and subsequent deagglomeration process was thenrepeated using a second 10 kilogram batch of dewatered pigment particlesto give product that was labeled as Sample C2 and that possessed anOTES-derived carbon content of 0.293 wt %.

Comparative Example 4

The dewatering procedure outlined in Comparative Example 3 was repeatedwith the following exception: another 55 kilograms of the startingpigment were passed through the rotary calciner but the calcinertemperature employed was 410° C. The pigment residence time was stillkept at 5 minutes. Thermogravimetric analysis of the resulting dewateredpigment particles yielded a moisture content of 0.50 wt %.

Ten kilograms of the dewatered pigment particles were then OTES-treatedand deagglomerated using the same procedures as described in ComparativeExample 3 to yield a final product that was labeled as Sample D1 andthat possessed an OTES-derived carbon content of 0.227 wt %.

The OTES treatment and subsequent deagglomeration process was thenrepeated using a second 10 kilogram batch of dewatered pigment particlesto give product that was labeled as Sample D2 and that possessed anOTES-derived carbon content of 0.308 wt %.

Comparative Example 5

Ten kilograms of the starting pigment utilized in Comparative Example 3were treated with OTES and then deagglomerated using the same proceduresas described in said Example to yield a final product that was labeledas Sample E1 and that possessed an OTES-derived carbon content of 0.296wt %. Prior to the OTES addition, the starting pigment was found bythermogravimetric analysis to possess a moisture content of 0.99 wt %.

The OTES treatment and subsequent deagglomeration process was thenrepeated using a second 10 kilogram batch of starting pigment to giveproduct that was labeled as Sample E2 and that possessed an OTES-derivedcarbon content of 0.302 wt %.

Example 6

Samples A1 through E1 were evaluated for their photoactivity behavior(750 exposure hours) using an in-house developed gloss retention test,the results from which are presented in Table 1. Said test involvedindividually compounding the above indicated samples as well as anOTES-treated, photoactive titanium dioxide based control pigment (onethat did not possess a metal oxide derived particle encapsulation) intopolyethylene (NA206, Equistar) using a batch internal mixer (FarrelBanbury® BR1600) at a 50 wt % pigment loading (76 vol % fill factor).After being mechanically ground into approximately ¼ inch (0.64 cm)pieces, the resulting masterbatches were then individually let down at420° F. (216° C.) to a 10 wt % sample (or control pigment) loading withinjection molding grade polypropylene (Montell PH-920S) using aCincinnati-Milacron (Vista VT85-7) injection molder. The molder-produced1% inch×3 inch×⅛ inch (4.45 cm×7.62 cm×0.32 cm) chips were analyzed forinitial gloss (average of readings from the top, middle and bottom ofthe to-be-exposed side of each chip) using a Byk-Gardener Gloss-Hazemeter. Said chips were then weathered in an Atlas Ci65A xenonWeather-Ometer® in accordance with ASTM Method G26-92 (Annual Book ofASTM Standards, Volume. 6.01, G26-92, 310-318, (1999)). To eliminatewater spotting, water with a minimum resistance of 12 megaohms was used.At periodic intervals, the chips were removed from the Weather-Ometer®,dried, and re-analyzed for surface gloss, the loss of which results fromthe titanium dioxide pigment catalyzed photo-degradation of the chippolymer matrix. Reduced gloss retention equates with enhancedphotoactivity.

TABLE 1 % Gloss Dewatering OTES- Retention Conditions Derived after 750TiO₂ Particle for Starting Carbon Exposure Sample Encapsulation PigmentContent Hours Photoactive None Not 0.305 wt % 29 Control dewatered A1Amorphous 338° C. for 0.298 wt % 61 Alumina 5 minutes B1 Amorphous Not0.288 wt % 62 Alumina dewatered C1 Amorphous silica/ 330° C. for 0.301wt % 72 boehmite alumina 5 minutes D1 Amorphous silica/ 410° C. for0.227 wt % 70 boehmite alumina 5 minutes E1 Amorphous silica/ Not 0.296wt % 72 boehmite alumina dewatered

A comparison of the gloss retention data for samples A1 and B1 revealsthat the low photoactivity performance of the amorphous aluminaencapsulated starting pigment was not compromised by the dewateringprocess. Comparing the gloss retention data for samples C1, D1 and E1allows one to reach the same conclusion for the amorphoussilica/boehmite alumina encapsulated starting pigment.

Example 7

Samples A2 through E2 were evaluated for their thin film lacingpropensity along with lacing and non-lacing control samples using anin-house developed test, the results from which are presented in Table2. The lacing control sample consisted of titanium dioxide particlesproduced according to Example 1 of U.S. Pat. No. 4,460,655, the contentsof which are incorporated herein by reference, which were then treatedwith OTES. The non-lacing control sample consisted of OTES-treatedtitanium dioxide particles that did not possess a metal oxide derivedparticle encapsulation. Said test involved individually compounding theabove indicated samples into polyethylene (NA206, LyondellBasell) usinga batch internal mixer (Farrel Banbury® BR1600) at a 50 wt % pigmentloading (76 vol % fill factor). The resulting pigment masterbatches werethen mechanically ground into approximately ˜¼ inch (0.64 cm) pieceswhich were then dried for 2-4 hours at 85° C. The dried and groundmasterbatches were then individually combined by hand with low densitypolyethylene (NA345, LyondellBasell), which had also been dried for 2-4hours at 85° C., to give mixtures with a 15 wt % sample loading. Eachmixture was then converted into approximately 100 mm wide, 50 micronthick ribbons of pigmented polyethylene film using a Thermo Haake singlescrew extruder (Rheomex 252, 19.05 mm screw diameter, screw length/screwdiameter=25) using barrel temperatures that ranged from 392° F. to 572°F. depending on barrel location and three different slit dietemperatures, specifically 560° F., 580° F. and 600° F. After cooling,the extruded ribbons were then examined for signs of lacing using thebelow indicated visual rating scheme. Note that a 10+ rating is the mostdesired and that ratings below 10 are generally considered to becommercially unacceptable.

Lacing Visual Rating Scheme

-   -   10+No→indications of a pre-lacing condition (dark striations) or        lacing (elongated thin spots or holes).    -   10→No elongated thin spots or holes, but pre-lacing signs are        present.    -   8→Presence of a few very small elongated thin spots or holes.    -   6→Presence of numerous small elongated thin spots or holes.    -   4→Presence of numerous large elongated thin spots or holes.    -   2→Total film is covered with elongated holes.    -   0→Film break is caused by complete loss of film integrity.

TABLE 2 Film Extrusion Temperature (Slit Die) Dewatering OTES- (15 wt %TiO₂, Conditions Derived 50 μm film thickness) TiO₂ Particle forStarting Carbon 560° F. 580° F. 600° F. Sample Encapsulation PigmentContent (293° C.) (304° C.) (316° C.) Non-Lacing None Not  0.30 wt % 10+10+ 10+ Control dewatered Lacing Amorphous Not  0.26 wt % 6 4 1 ControlAlumina dewatered A2 Amorphous 338° C. for 0.312 wt % 10+ 10+ 7 Alumina5 minutes B2 Amorphous Not 0.319 wt % 8 8 5 (starting Alumina dewateredpigment) C2 Amorphous silica/ 330° C. for 0.293 wt % 7 6 4 boehmitealumina 5 minutes D2 Amorphous silica/ 410° C. for 0.308 wt % 8 8 5boehmite alumina 5 minutes E2 Amorphous silica/ Not 0.302 wt % 7 6 3(starting boehmite alumina dewatered pigment)Inspection of the data contained within Table 2 shows that startingpigment that is encapsulated with amorphous alumina and starting pigmentthat is encapsulated with amorphous silica/boehmite alumina, samples B2and E2, respectively, both inherently possess poor lacing resistance. Inthe case of sample B2, the dewatering conditions utilized (5 minutes ofheating at 338° C.) significantly increased its lacing resistance(compare the lacing resistance performance for sample B2 to that ofsample A2). More specifically, for the two lowest film extrusiontemperatures evaluated (560° F. and 580° F.), the lacing resistanceincrease was sufficient (10+ final lacing rating) to allow the use ofthe dewatered pigment (after OTES treatment) for the production of, forexample, lacing-free thin films.

Unexpectedly, however, the utilization of essentially the samedewatering conditions, viz. 5 minutes of heating at 330° C., as for thedewatering of sample B2 did not result in a significant improvement inthe lacing resistance of sample E2 (compare the lacing resistanceperformance for sample E2 to that of sample C2). Surprisingly, theutilization of even more severe dewatering conditions, viz. 5 minutes ofheating at 410° C., still did not impart to sample E2 a useful level oflacing resistance (compare the lacing resistance performance for sampleE2 to that of sample D2).

We claim:
 1. A method of making a masterbatch comprising the steps of:a) providing titanium dioxide particles encapsulated with amorphousalumina; b) heating the titanium dioxide particles encapsulated withamorphous alumina to a temperature above 100° C. to form dewateredparticles; c) treating the surface of the dewatered particles with anorganic compound to form treated particles; and d) mixing the treatedparticles with a thermoplastic polymer to make a masterbatch.
 2. Themethod of claim 1 wherein the titanium dioxide particles are heated to atemperature in the range of 200° C. to 500° C.
 3. The method of claim 1wherein the organic compound is selected from the group consisting oflow molecular weight polyols, organosiloxanes, organosilanes,alkylcarboxylic acids, alkylsulfonates, organophosphates,organophosphonates and mixtures thereof.
 4. The method of claim 1wherein the organic compound is selected from the group consisting oflow molecular weight polyols, organosiloxanes, organosilanes andorganophosphonates and mixtures thereof.
 5. The method of claim 3 wherethe organic compound is present at a loading of between 0.20 wt % and2.00 wt % on a total particle basis.